Idea problem record

newly build web After the project, click helloservlet Later error reporting ?

Mine is because tomcat Version issue for , from 10 Switch to 9 There is no problem

css The file is invalid or changed css Restart after file is invalid ?

problem : Modify anyway css file , start-up idea After that, there was no effect , Unless put css Write directly in html in
browser : Google
Delete first idea In the project target file
Then delete the browser cache
Restart again to reflect the effect in time
Without rhyme or reason
…
I yue 了

The certificate is not trusted ?

No crack idea, I applied with my student card …
result

But everyone on the Internet is talking about cracking …"~%?..,# *'*&℃$︿*?"
I don't know why

jsp in java Code section out Not available print Method ?

In addition to other blogs on the Internet
stay webapps Create a folder by yourself lib Then import outside the project
Just when you start a new project
hold full platform Just tick it
I don't know which one works

How to import Mysql drive

Download url

Click on download

Unzip it after downloading
open idea

Then import the whole unzipped file
apply That's all right.
A test sample

package day01;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class DB1 {
    

    public static String driver="com.mysql.cj.jdbc.Driver";
    // Need to change your user name and password 
    public static String user="root";
    public static String password="xxxx";


    public static void main(String[] args) {
    
        // Create database 
        try {
    
            Class.forName(driver);

            Connection con1;
            String url1="jdbc:mysql://localhost:3306";
            try {
    
                con1 = DriverManager.getConnection(url1, user, password);
                Statement statement=con1.createStatement();
                statement.executeUpdate("create database mysql_db1");
                statement.close();
                con1.close();
            } catch (SQLException throwables) {
    
                System.out.println(" Yours SQL The sentence is wrong ...");
            }

        } catch (ClassNotFoundException e) {
    
            System.out.println(" There's something wrong with the drive ");
        }

    }
}